This section is intended to provide a background to the various embodiments that are described in this disclosure. The description herein may include concepts that could be pursued, but are not necessarily ones that have been previously conceived or pursued. Therefore, unless otherwise indicated herein, what is described in this section is not prior art to the description and/or claims of this disclosure and is not admitted to be prior art by the mere inclusion in this section
In a typical cellular radio system, user equipments (UEs) (also known mobile terminals, terminals, user terminals, wireless terminals, wireless communication devices, wireless transmit/receive units (WTRUs)) can communicate via a radio access network (RAN) to one or more core networks (CN). The radio access network (RAN) covers a geographical area which is divided into cell areas, with each cell area being served by a base station, e.g., a radio base station (RBS), which in some networks may also be called, for example, a “NodeB” (UMTS) or “eNodeB” (LTE). A cell is a geographical area where radio coverage is provided by the radio base station equipment at a base station site. Each cell is identified by an identity within the local radio area, which is broadcast in the cell. The base stations communicate over the air interface operating on radio frequencies with the UEs within range of the base stations.
In some versions of the radio access network, several base stations are typically connected to a controller node (such as a radio network controller (RNC) or a base station controller (BSC)) which supervises and coordinates various activities of the plural base stations connected thereto. The radio network controllers are typically connected to one or more core networks.
The Universal Mobile Telecommunications System (UMTS) is a third generation mobile communication system, which evolved from the second generation (2G) Global System for Mobile Communications (GSM). UTRAN is essentially a radio access network using e.g. wideband code division multiple access (WCDMA) for UEs. In a forum known as the Third Generation Partnership Project (3GPP), telecommunications suppliers propose and agree upon standards for third generation networks and UTRAN specifically, and investigate e.g. enhanced data rate and radio capacity. The 3GPP has developed specifications for the Evolved Universal Terrestrial Radio Access Network (E-UTRAN). The Evolved Universal Terrestrial Radio Access Network (E-UTRAN) comprises the Long Term Evolution (LTE) and System Architecture Evolution (SAE). Long Term Evolution (LTE) is a variant of a 3GPP radio access technology wherein the radio base station nodes are connected to a core network (via Access Gateways, or AGWs) rather than to radio network controller (RNC) nodes. In general, in LTE the functions of a radio network controller (RNC) node are distributed between the radio base stations nodes (eNodeB's in LTE) and AGWs. As such, the radio access network (RAN) of an LTE system has an essentially “flat” architecture comprising radio base station nodes without reporting to radio network controller (RNC) nodes.
Movement of UEs Between Cells
Session Continuity is a concept for using the so-called Release with Redirect mechanism and a method to move a UE between cells in a network while in the so-called connected mode. The cells may exist for the same radio access technology (RAT) or for different RATs. Release with Re-direct is a standardized (3GPP) procedure to perform such a move within a RAT or between RATs.
The mobility mechanism ‘redirection’ has existed for a number of years in the 3GPP standardization and can be seen as a complement to the traditional idle mode cell reselection mechanism and the network triggered handover mechanism. Redirection moves a UE rapidly to another frequency and/or RAT in order to retain service, for example when the UE is moving outside radio coverage. Redirection is also specified as one of the methods utilized by the so-called CSFB features (Circuit Switched Fallback).
The basic concepts for redirection can be summarized as follows: Redirection is generally network triggered—as is also the principle in the earlier-mentioned mechanism for handover. When using Redirection the UE is generally not directed to a specific cell, and no resources are reserved beforehand. This means that the source network (or, rather, the source RAN node) leaves it up to the UE to find the best cell and to continue the service there—i.e. similar to the principle behind cell reselection. The network (or, rather, a RAN node) can trigger a redirection based on, e.g, radio coverage reported by the UE after certain UE measurements. Alternatively, the network can trigger the redirection based on statically configured frequency neighbor relations.
With some of the current technologies, when a UE is moved from one (source) cell controlled by a (source) RAN node to another (target) cell in a (target) RAN node (e.g., according to the same RAT or different RATs) the target RAN node does not generally know from where the UE is moved. Moreover, the source RAN node does not generally know exactly to which target RAN node the UE is moved to. This is, for example, true when a so-called Release with Re-direct procedure is used.
This may give rise to a number of challenges for the network:                Observability of success rate of the move is generally not possible since the success rate is number of successful attempts divided by number of attempts and the number of attempts may only be counted in the source RAN node whereas the number of successful attempts may only be counted in the target RAN node. Typically, observability counters or similar functionality are typically configured to count on a per cell relation basis. When the source RAN node does not know exactly to what cell the UE is moved, this source RAN node cannot count this per cell relation. Also, when the target RAN node does not know what cell the UE is moved from, the target RAN node can not count this per cell relation either.        Network optimization is generally not possible. A network and/or operator cannot optimize the conditions for UE moves between cells, since the network and/or operator does/do not generally know between what cells these moves are currently made.        Automatic network tuning is generally not possible.        
More particularly, when the UE is re-directed by means of Release with Redirect, the UE will generally search for a target cell in a requested RAT and, if the UE finds a cell with good enough quality, it will attempt to access that cell. The principle in the existing standardized solution generally as follows: When an UE is accessing the selected cell this target cell cannot tell whether the UE is accessing this selected cell due to a network triggered redirection or if it is due to a UE triggered cell reselection. For example when a UE is re-directed in either direction LTE->UTRAN (i.e. from LTE to UTRAN) or UTRAN->LTE (i.e. from UTRAN to LTE) there is no information given to the target network (or, rather, a RAN node of the target network) that the UE was redirected. Without this information the target RAN node cannot, for example, avoid rejecting or redirecting the UE back to the source cell. Moreover, since there is no possibility to observe how successful the redirects are there is also no way for the network to improve the success rate. Further, no input for neither self-optimization (SON) mechanisms nor for manual tuning by network configuration is generally available.
Related 3GPP Specifications
The following sections of a non-exhaustive list of 3GPP technical specifications may be applicable to the technology disclosed herein as a technology background:                3GPP TS 25.331 V.11.3.0 (2012-September): Chapters 8.1.3 “RRC Connection Establishment” and 8.1.4“RRC Connection Release”.        3GPP TS 25.413 V.11.1.0 (2012-September): Chapter 8.34 “Direct Information Transfer”.        3GPP TS 36.331 V.11.1.0 (2012-September): Chapters 5.3.3 “RRC Connection Establishment”, 5.3.8 “RRC Connection Release” and 6.2.2.Message definitions.        3GPP TS 36.413 V.11.1.0 (2012-September): Chapter 8.13 “eNB Direct Information Transfer”.        